Selective calling system



3 Sheets-Sheet 1 ATTORNEY I M/VEIVTUR A. WEAVE A. WEAVER SELECTIVECALLING SYSTEM Filed Aug. '28, 1942 y 1, 19454 A. WEAVER SELECTIVECALLING SYSTEM Filed Aug. 28, 1942 3 Sheets-Sheet RNEV m R R. A w. A W

May 1, 1945. V A. WEAVER SELECTIVE CALLING SYSTEM Filed Aug. 28, 1942 5Sheets-Sheet 3 m/vavron B WEA VER Patented May 1, 1945 UNITED STATESPATENT "OFFICE 2,374,908 SELECTIVE CALLING SYSTEM Allan Weaver, PortWashington, YL, assignor to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application August 28, 1942,Serial No. 456,571,

' lSClaims. (01.178-2) Thisinvention relates to a selective callingsystem and particularly tosuch a system in which a plurality of stationsto be selectively called are associated with a common signaling channel.

An object of the invention is to transmit selective station callingsignals and telegraph message signals over the same communicationchannel.

Another object of the invention is to render the selective station callreceiving apparatus unresponsive to telegraph message signals.

The invention features at the calling station ,a pulsing dial and apulse divider circuit whereby only one signaling current'transitionoccurs on each pulsing cycle of the dial contacts.

The invention also featuresat eachof the selectively callable stationsat call: responsive step-bystep selector which is disabled duringintervals of idleness of the signalin channel and is also disabledduring the transmission of telegraph siglittle on the channel and whichbecomes qualified to respond to selective calling signals in stepbystepmanner under the control of timing apparatus which becomes effectiveonly after a signal of'a predetermined character has beenimpressed uponthe signaling channel for a predetermined interval.

In accordance with the preferred embodiment of the invention the systemincludes a principal or call initiating" station having station callingsignalgeneratingapparatus and also having telegraph signal transmittingand receiving apparatus, and a plurality of subordinateor outlyingstation's having selective station call signal receiving apparatus andalso having telegraph-signal receiving and transmitting apparatus; Allof the stations are associated'with a closed loop type of signalingchannel which has at least one source of signaling potential associatedtherewith.

At the principal station the selective station call signal generatingapparatus comprises a system of relays controlled by a pulsing dial soas to impress markin and'spacing signals on the signaling channel at therate of one transition from marking to spacing-or from spacing tomarking for eachcomplete cycle of the pulsing contacts of the dial. Thestation also has telegraph signal transmitting contacts and the selectormagnet of'aprinting telegraph receiving recorder associated with thesignaling. channel for transmitting and receiving telegraph signals.

At each of the outlying or subordinate stations a signal responsivere1ay,.a set. of telegraph signal transmitting. contacts and-theselector magnet of a printing telegraph receiving recorder areassociated with the signalingchannel The signal receivingrelay controlsa.stepby-stepse1ectorand andfthe stepby-step selector at each of the.out-j lying stations is disabled. The disabling relay, when operated,is controlled by the signal receiving relay and has a slow-releasecharacteristic so that it" will beheld energized by marking current onthe signaling channel and willnot be released until there has been aspacing signalonthe channel of a duration longer than that of thelongest spacing'interval normally occurring in telegraph signaltransmission.

In the operation of the system an attendant at the principal stationdesiring to call one of the outlying stations operates a break key,which impresses a spacing'condition on the signaling channel, forasufficient interval to release the selector disabling relays at alloutlying stations. The attendant then transmits by means of the dial thecalling code for the particular station and this code operates thestep-by-step selectors at all of the outlying stations to advance theselectors, but'iat only one of the stations will the selectorbeadvanced' tosuch position that it will completethe circuit for a callindicator to inform an attendant at the particular outlying station Ithat telegraphic communication With maceration is desired.

However, upon the beginning of transmission of telegraph signals; suchas when an attendant at the called station operates the telegraph signaltransmitting contacts thereat to transmit char acters" representing ananswereback, the short spacingi'mpulses which such signals will containare effective: to cause the timing mechanism to operate the selectordisabling relay at. that station andat all other stations.

For aco'mplete understanding of the invention, reierence mayybe had: tothe following detailed description to be interpreted in the lightalsocontrols atiming circuitincluding-a plurality of relays one-ofwhich-isarranged to disable the step-by+step-selector.. a

In the idle-condition of'the apparatus follow of the accompanyingdrawings wherein:

latter" being represented symbolically;

Fig. 2 i's a circuit diagram showing" a third-subordinate station infull detail;

Figs. 3, 4 and 5 are circuit diagrams showing alternative arrangementsof apparatus to be controlled by the step-by-step selector at asubordinate station; and

Fig. 6 is a diagrammatic view showing how Figs. 1, 2 and 3, Figs. 1, 2and 4, and Figs. 1, 2 and 5 are to be interassociated to reveal thecomplete selective calling ystem provided with any of the three types ofselector controlled apparatus.

Referring now to the drawings, and particularly to Fig. l, the brokenline rectangle H designates the principal station of the system. Fromthe station H signal transmission line conductors l2 and 93 extend outto the subordinate stations, and the line conductors l2 and I3 areinterconnected at the station ll through a loop which includes break keyI6, the normally closed upper pair of contacts of a dial key I'I,signaling battery i8, telegraph signal transmitting contacts 58 and theselector magnet 2| of a printing telegraph recorder, which may be of thetype shown in Patent 1,745,633 granted December 23, 1924, I

to S. Mortion et al., or may be of the type shown in Patent 1,904,164granted April 18', 1933, to S. Morton et al.

The dial key IT has a pair of normally open contacts, namely, the lowercontacts shown in Fig. 1, through which a source of alternating currentmay be connected across the input terminals of a full wave rectifier 22which provides at its output terminals a source of direct current. Afilter condenser 23 is connected across the output terminals ofrectifier 22 for filtering out the alternating current components at theoutput of the rectifier.

Upon the operation of the dial key I! the loop interconnecting the lineconductors I2 and I3 is opened at the upper dial contacts and the sourceof alternating current is connected across the rectifier 22 at the lowerdial contacts. When the rectifier 22 has been energized, a circuit maybe traced from the right-hand output terminal of the rectifier throughthe single pair of pulsing contacts of dial 24, which contacts areclosed when the dial is at rest, through the right-hand armature andback contact of a relay 26, righthand armature and back contact of arelay 2'! and winding of a relay 28 to the left-hand output terminal ofthe rectifier. Over this circuit the relay 28 becomes energized.

At its outer right-hand armature and front contact the relay 28 reclosesthe transmitting line loop which was opened at the upper contacts of thedial key l1. At its inner right-hand armature and front contact therelay 28 prepares an energizing circuit for the left-hand or operatingwinding of relay 26 in series with the winding of relay 28 but theoperating winding of relay 26 is at this time short-circuited by theclosed dial contacts so that the operating winding of relay 26 does notbecome energized. At its lefthand armature and back contact, relay 28opens a circuit from the. right-hand output terminal of rectifier 22through the left-hand armatureand back contact of relay 21, left-handarmature and back contact of relay 28 and resistor 29 to the left-handoutput terminal of rectifier 22. Resistor 29 and th winding of relay 28preferably have the same resistance value so that with either thewinding of relay 28 or the resistor 29 connected across the output ofrectifier 22, the drain on the rectifier will be the same. It is forthis season that the relay 28 upon being energized disconnects resistor29 from across the out,- put terminals of the rectifier 22.

The selective calling code signal generator is now in condition for thetransmission of a calling signal by means of dial 24. However, in orderto place the outlying stations in condition to respond properly to theselective station calling signals, it is necessary to impress a longspacing signal on the signaling lines' l2 and IE to perform operationswhich will be described later. The transmission of the long spacingsignal may be accomplished by opening the break key I6. It is necessaryto do this because although the upper contacts of the dial key I!impressed a spacing signal on the line conductors, the relay 28 becameenergized and immediately shunted the open dial key contacts by means ofit outer right-hand armature and front contact so that the spacingsignal thus briefly impressed upon the line conductors may not be ofsufi'icient duration to accomplish the desired result at the outlyingstation.

Following the reclosure of the break key l6 to terminate the longspacing ignal, dial 24 is operated by rotating it in well-known mannerto advance the dial to the position corresponding to the first digit ofthe calling code to be transmitted. The dial contacts 24 remain closeduntil I the dial is released to permit it to return to the normalposition, during which return the calling code impulses are transmitted.The dial cone tacts open and reclose once for each element or unit ofthe digit so that if the digit i 8, for example, the dial contacts willopen and close eight times whereas if the digit is 5, for example,the.dial contacts will open and close five times.

Upon the first opening of the dial contacts, the shunt across theoperating winding of relay 26 is removed, so that the relay 26 becomeenergized through its operating winding in series with the winding ofrelay 28 over a circuit previously traced. At its right-hand armaturerelay 26 transfers the dial contact connection from the armature ofrelay 2! through which relay 28 was originally energized and connectsthe now open dial contacts to one terminal of its holding winding, theother terminal of which is connected to the left-hand output terminal ofrectifier 22, and also connects the dial contacts to one terminal of thewinding of relay 21, the other terminal of which is connected throughresistor 3| to the left-hand output terminal of rectifier 22.

At its left-hand armature and front contact the relay 26 connects aresistor 32 across the output terminals of rectifier 22 in shuntrelation to the operating winding of relay 2'6 and the winding of relay28, which are now in series, and

' whereas the placing of the operating winding of relay 26 in serieswith the winding of relay 28 tends to reduce the drain on the rectifier22, the resistor 32 draws sufiicient additional current to hold thetotal drain on the rectifier at the same value as it was when resistor29 or the Winding of relay 28 was connected across the rectifier. Sincethe relay 28 has remained energized, the loop across the line conductorsl2 and I3 has remained closed so that no change has occurred in thecondition of the line conductors as a result of the opening of the dialcontacts.

Upon the first reclosure of the dial contacts the energizing circuitsfor the holding winding of relay 26 and for the winding of relay 2? arecompleted in parallel from the output terminals of rectifier 22. Thusthe relay 26 remains energized and the relay 2! at its right-handarmature and back contact interrupts the energizing circuit for theoperating Winding of relay 26 and for the Winding of relay 28. At itleft-hand armature 2,3114, one:

and back contact; the relay- 21; opens the circuit for resistor: 29;.which: haspreviously been opened at the left-handarmature; and back:contact of relay ZB-so: thatthe. resistorifliwill not be ccnnectedacross the output of. rectifierZZ upon the releaseotrelayZB whichtheenergization of re lay 2'! has caused: Three conductive-paths are nowconnected across the output on the a rectifier 22, these bein theresistor 32' the: holdings/ind: ing' of relay 26-and the winding: ofrelay 2'! with the resistor 3.! in: series with-it. The-resistance:

values of the holding. winding of relay; 2.6, of re-- sistor 3.1 and:the Winding of: relay. 2'!" in: series. and of resistor 32; ar suchtthatthe aggregate resistance. of the three parallel path in theex be:apparent thatodd-numbered closures" of the ternal circuit of rectifier;22: is equal to the re rupted so that this circuit willnot be; reestabslished when relay 2-6 is released! At its left hand armature and. back.contact. the; relay 2!! again preparesv for" the connection of resistor29 across the outputterminals of'the rectifier. the path now being openat the left hand armature and backcontact of relayzl. '5 l Upon; thesecond opening of the dial contactsthe energizing circuits. fontheholding windin 3. opening}. ofthe" dial-i contactsrelays 26. and; 2 1.-are releasedzrandz the; direct energizing; circuit for. relays 2831s:preparedi. Upon; the fourth, closing of the: .dial! contacts; relay 28becomes energized to restore: the-line: conductors; I 2 y and L3 tomarking. the: foregoing. it will be apparent that onht'thaiclosuneandmct. the: opening of the. dial contactsiis eifective to cause alinecurrent transiftionbnr the: lineaconductors tizandg 31 v,Thus

there are only halfrasimany: line current transitime: as; dial: contacttransitions; and: the system maybe; said? to: be a: pulse. divider. It'will also dial. contacts: change the. charactenof the signal on: theline from; that. which existed: beforeathe dial was; operated and:even-numbered dial. contact: closure restore the line condition to thatwhich existed beforezthe dialswas operatedi. Ac.- cordingly; whenlanoddtnumber-isdialed the line condition will be different when the dialcomes to rest from that whichyexisted-before the dial was operated": andwhen an even. number isdialed the line condition will be the same whenthe dial comes to rest as thatwhich existed before the dial' wasoperated; If a. calling signal consists of two digits and bothareoddnumbers. ornboth are-even numbers; the' -line conductorswill be inn marking condition whenthe dial comes to rest after the transmissionofthe-second digit, whereas if one only of the digits is an odd number,the line conductorswill be in the spacing condition when thediaireturn's to rest after the second digit.

Following thetransmission ofithe selective sta tion calling signal;which is not limitedto one or two digits but may=beofthree or fourdigits, de-

of relay 25 and for the winding of relayllsreinterruptedso that-theserelays are released. right-hand armatures of. the: relays 26 and 21.again nrepare the direct energizingi circuit for: the relay 28 throughthein right-handbook contacts but this energizing path is nowinterrupted at the open dial. contact. At its lefteh'andarma--. ture therelay zfi disconnects resistor iizafrom: across the output terminal ofthe rectifierrwhile at the left-hand armature and-back contact of: relay21, resistor 29 is reconnectediacross the, output terminals of therectifier" to mainta n con stant drain on the rectifier during-thenterval that none of the relays 25, 2''! or: 28' isenergizcd. Thecondition or line conductors; t2: and liihas o ee cha ed due; to thesecond} opening: of. the dial. contactsv because relay 28. has:remained: deenergized. i

Upon the second closing; of the dia'lacontacts the relay 28 becomesenergized. over thefirst-described directenergizing; circuitandlrecloses the loop across the lineconductorsalll and I3; .The relay28 also disconnects resistorzfi from. across the rectifier 3.2 andagain: prepares for. the ene1.- gization ofthe operating w ndine ofrelay 2-55 inseries with the winding of relay 285. Thex opena-t ngwinding of relay 25. is atthistime shunted by the now closeddialcontacts.

Upon the third openingsor the dial-contacts relay Zfibecomes energizedinseriesiwith. relay 28: and again prepares for: the energization of itsholding winding. and for, the energization of relay 21. Upon, the thirdclos ng of diatcontacts relay 2! becomes. energized. tofirelease-irelay218 and relay 2'5 remains energized-through itsholding winding. Thus asecond spacing signal is impressed upon the line conductors liiand {itdue to. the release. of. relay 28. Upon: theifflurflfb pending upon thenumber of stations contained in the system; the-dialkeyx I1 isrestored'to normal.' At its upper contacts the loop across the lineconductorst7. and l 3-is reclosed and at'its lower contacts powerisdisconnected from the rectifier 22 i so that all relays are releasedandthe system is restored sc the-initial condition. From this-it will beapparent that the line conductors l2 and- [3 are aiwaysinmarkingcondition following the operation of dial key ll in preparationfor the transmission" of a selective calling responsive relay 12* allinseries-at-station 36, then through selector magnet: 03; transmittingcontactsMLand signal responsive-relay 46- allfinseries at: station alland then through selector magnetdh transniittingcontacts 4B'and'signal responsive relayi-dilalliin series-at station 3B (Fit-:52),liiine conductor l3extends-on beyond station- 38 and may include theselector" magnets, transmitting contacts and signal responsive relaysof' other stations and is: eventually interconn ected through a loopWitjhrline conductor 12 which n1aya]so-ineludeselector-magnets;transmitting contacts and signal responsivc;relays ofother-outlying or sub.- ordinaterstations;

ReierringLnow' particulanly to FigLlZythe-stw- 131011138: has awmotor 5ifor: driving the printin'gl telegraph receiving recorder controlled byselector magnet 4! and also for operating transmitting contacts 48.Power is applied to motor 5| from a source of alternating currentthrough a switch 52, the normal condition of which is open and. which isclosed by an attendant when the station is to participate inintercormnunication with the principal station H. The stations 36 and 31have. similar motors 53 and 54 controlled by switches 56 and 51,respectively. 1

Since the selector magnets and signal responsive relays are inseries'with-the line conductors at all stations, these elements respondto and follow all signals, whether such signals are telegraph signals orselective station calling signals generated at the principal station II,or whether they are telegraph signals generated at any of the outlyingor subordinate stations.

At the station 38 the upper and lower contacts of the signal responsiverelay 49, which are the marking and spacing contacts respectively, areconnected to the positive and negative conductors BI and 62,respectively, of a power supply comprising a half waverectifierincluding the upper anode and cathode of a discharge tube 63connected so that the discharge path between the anode and cathode isbetween the positive conductor 6| and one side of a source ofalternating current, the negative conductor 62 being connected directlyto the other side of the source of alternating current. A filtercondenser 65 is connected between conductors 5i and 62 for filtering outalternating components at the output of the rectifier. 'I'ne armature ofsignal responsive relay 4S is connected through a condenser 64 to oneside of the operating magnet 66 of a step-bystep selector 6?. The otherside of the magnet 65 is connected to the lower armature of a relay 68.

The step-by-step selector 5'! may be of the type shown in Patent1,345,256 granted June 15, 1920, to J. C. Field and the disclosure ofthat patent is incorporated herein by reference as part of the presentspecification. Briefly, such a selector consists of a polar magnethaving an armature which is rocked clockwise or counter-clockwise from acentral or neutral position in response to polar impulses of .current.The armature is provided with an arm which operates a pawl mechanism forstepping a contact wheel or disc and the disc is advanced two steps foreach full cycle of oscillation of the armature lever, by which is meantfrom the neutral position to one side, then to the opposite side andback to the neutral position. The contact wheel or disc is provided withselectively located pins which will be engaged by a check pawlcontrolled by the armature lever when the armature lever is momentarilypermitted to be at rest in the neutral position after having beenoperated through a plurality of cycles or half cycles, and such pawlprevents the contactdisc or wheel from returning to normal positionunder the influence of its restoring spring. When a plurality of suchselectors with difierently located stop pins respond to signalsconsisting of current reversals, a pause in the transmission of signalswill cause those which have stop pins presented to their check pawls tobe held in the positions to which they have been advanced, whereasall'selectors which have no stop pins in those positions will return tonormal position under the influence of the disc restoring springs. Whentransmission of current reversals is resumed those discs which were heldin advanced positions are further advanced from those positions, whereasin all of. the selectors the discs of which were restored to normal,those discs are again advanced from the normal position.

Step-by-step selectors of the type disclosed in the patent to Field areprovided with contacts which are engaged by a contact arm carried by thestep-by-step wheel or disc for the completion of electrical circuits.The electrical circuits are completed through the check pawl as acircuit element, 501 that as the contact arm comes into engagement witha contact, as it is being advanced step by step, an electrical circuitis not completed if the advance continues but only if there is a pausein the signal train which permits the check pawl to engage a stop pinand hold the disc or wheel in the position to which it has beenadvanced. When selectors of this type are employed in a system, all mayhave their electrical contacts in the same relative positions, such asin the eleventh, thirteenth, fifteenth and seventeenth steps. Taking thethirteenth step as an example, it is not necessary to send thirteenimpulses in regular succession in order to cause the selector to reachthat position. The selector may be provided with one or more stop pinsintermediate the rest position and the thirteenth step whereby thethirteenth step may be reached by the transmission of sets of impulseswhich total thirteen, with a pause between each two sets of impulses.During the pause at the end of the first set of impulses, thoseselectors which have stop pins in the position to which the discs of allof the selectors have been advanced will be held and the discs of theremaining selectors will be restored to normal. In a two-digit systemonly one disc would be so held and all of the others would be returned.In a three-digit system, a plurality of discs would be held and theremainder would be restored to normal. Upon the resumption oftransmission of impulses, all of the selector discs would again beadvanced, some" from their initial positions and one or more fromitsadvanced position. At the end of the second group of impulses the discof one selector closes an electrical circuit, if the system operates ona two-digit call, and all of the remaining discs return to their normalpositions, with the exception that the second set of impulses maycorrespond to the first digit for some other selector in the system andthe disc of that selector may beheld in its first digit positionalthough it will close no electrical circuit in this position. Followingthe closure of the electrical circuit by the disc or wheel of theselector, the transmission of a single impulse will restore all of theselectors to normal. If the system is operable upon a three-digit call,a plurality of discs will be held at the end of the second set ofimpulses, the number being smaller than the number which were held atthe end of the first set of impulses. At the end of the third set ofimpulses only one of the discs will have been advanced to a position toclose an electrical circuit.

In the arrangement shown in Fig. 2, when the relay 68 is deenergized,which is the condition following the transmission of a long spacingsignal preparatory to the transmission of selected station callingsignals, as will be described later, one side of the operating magnet 66of the stepby-step selectorfif! is connected to the negative conductor82 of the direct current power supply and the other side of magnet 66 isconnected through condenser 64 and through the armature and markingcontact of relay 49 to the positive conductor 6| of the power supply.This causes the condenser fl to be charged positivelyon the side towardthe-armature :of relay i9 and negatively on "the side toward magnet 66.When relay 49 goes to spacing, both sides of condenser 64 are nowconnected to the negative conductor B-Lpermitting condenser 64 todischarge through condenser is thus connected in parallel with resistorwhen :relay "If is sde'enengized.

For'the purpose of setting iorth the operation of the system ofcondensers associated with magnet "66 which roc'lrs the armature to oneside. i i

If the relay E9 returns to mar-king before the discharging current hasdied out, condenser fi l will be recharged and the charging current willcondenseriil liiniparallel with variableresistorzdh relay H, it will beassumed'tha't the lineicon doctors 12 and '13, having previously beeninmarking condition, :have gone to rspacing condition as, Ifor example,lupon transmission of the first spacing iimpulse 10f 1a selectivecallingcode. Relay 4:? goes to spacing and releases :relay l! which removes thelowtresistance shunt includ ing resistance 81 .from condenserrliziandconnects Condenser :82 isrroi relatively large capacity and ahighinitial charging current flows lthrough:re--' sistor 18 3. This producesa relatively high p0 line cond'uetors m and I3 =arenot polar-inthearrangementshown 'inFigs. 1 and 2 and there is no actual reversal ofbattery connection across the "magnet 66.

The armature of signal 'responsivegrelay lfdisl conne'ctedlthrough"conductors H, 1'2 "and '13 to 3 the upper armature of "relay 68 which,beingassumed to be released at this time, engages its back contact, fromwhich a circuit extends through resistor T4, shunted by a condenser '75,conductor 1'6, Winding ofrelay -71 and conductor power 18 to thenegative conductor 62 of the supply. Overtime circuit just "traced therelay tential difference across resistor 83 which is (also impressedacross condenser '34. condenserm becomesccharged,thechargingcurrentandtherefore lthewpotential difference "across :resistor '83 decreases andthe potential :difference across condenser 84 correspondingly"decreases.If the .relay ll .:sh:o1ild remain :rleased :under the control ofzzrelayrfis zuntil condenser "82 becomes :iully charged, the :fiow :ofcurrent ithroughiresistor 83 willrceaserand the potentialadiiference"acrosscc'on denser :84 ibe reduce'd ito zzero.

:Ilhe'tront icontact which the lower arma ture of :relay 11.1 is:engagealdlelwhen .the relay is energized, is connected by conductor :86to the grid of an :electrom'd'ischarge tube .81. Before M willfollow-the "operation of the armature of signal responsive relay '49,whether "that relay is following rapid telegraph signals or 'theslowerselective station calling signals generated by the dial controlled pulsedivider circuit in Fig, 1, the relayl'l being energized when thearmature of' relay 49 engages the marking contact and being deenergizedwhen "the armature of relay 69 engages the spacing contactfThe functionof condenser T5 is to accelerate the operation of relay 77. A resistor19 {having approximately the same resistancevalue as the aggregate ofresistor M "and the winding of relay '11 in seriesis .cfonnecterlbetween positive power supply conductor BI and the armature of relay 49through conductor 1! :to provide a drain on the power sup ply when thearmature 'of relay 49 engages the the llower armature \oflrelay :11!engages its :iront contact, the arid :ofltulbe 18! sis at the potential:of

the negativelpower supply conductor 6-2 by virtue of its connection tothat conductor through a resistor 88, and the cathode of tube 8 7 ismore positive than th :grid loy virtue =of the potential differenceacross a resistor BEl in a circuitT-rom the, negative power supplyconductor 62, lower back contact an-d :armature of a relay 9Icondujotors 92 and 93, resistors 89 :andpll l to the positive powersupply conductor '6 the cathod of tube 8 bei1rg-connected"tothepoint ofinterconnection "LOT resistors -89 and 94. Upon the engagement of {thelower arm'ature of relay "H with its front contact, which occurs when amarking impulse is impressed upon the line conductors spacing contact,whichiis connected tonegative 1 power supply conductor "62,substantially equal to "the drain through resistor '14 and the Wi-ridingof relay 1'! when the armature of relay 49 engages themarking contact.When the latter.

condition of the relay 4'9 exists, the resistor ill is short-circuitedby the armature and marking contact. a j y The upper armature of relay2.! is connected :to positive power supply conductor Bil through aresistor '81 and the upper front contactLi-s connected to thesameconductor through a condenser =82. The upper from contact is .alsoconnected .to the lower back contact and to one terminal of a variableresistor 8'3, the other terminal of which isconnected to the negativepower supply conductor "51. it willhelapparent from an examination ofFig. .2 that when relay "H is de energized condenser'lli is connected inseries with variable resistor d3 across the power supply conductors Eland 6'1 and condenser '82wil1nbeeome charged.

When relay "I? is energized condenser 8.2 will be discharged throughresistor 8 I. The'lowerg'armature of relay 1'! is connected throughcondenser 34' to negative power supply conductor 62 and the der whichthe tube is rendered conductive will.

t2 and f3, as for "example at the beginning of y a marking signalfollowing the 'firstspacin'g signal 'o'f the selectedsta'tion callingcode, "thepo tential of the grid of tube "81 is raised by the po tentialdifference across condenser 84. This potential will be smaller inmagnitude the longer the intervalduring which charging-current fiowed tocondenser 82 and the constants or the circuit-are-"such thatinsufficient potential difference appears across'condenser 84 atthe endof a spacing impulse of a selective calling code to render tube 81conductive. Accordingly, tube 8 remains 'nomcondu'ctiye during thereception of "a selective calling code and the circmnstances unbedescribed later. During the reception of the selected calling code, theselector discs of the selectors are .ad-V vanced step by Step at allstations and it will be assumedtliat the received code causesthesjel'ector disc at "thestation shown in Fig. 2 to advance its contactarm to "engagement with contact 101.

The check vpavvl I02 *o'ftheselector, whichgem gages and holds the "discin the position to which it has been advanced, is connected to thenegative power *supply conductor 62 so that it comp-letes a circuit fromthat conductor 'tm'ough the contact disc and contactann of the selectorto contact IIJI and from there through conductor I63, and assuming thatthe selector controlled system shown in Fig. 3 is associated with thestation shown in Fig. 2, through conductor 363, conductor I64, windingof relay I66, resistor It! and conductor ms to a positive power supplyconductor I69 which derives its positive potential from the cathode ofthe lower diode section of tube 63, the anode of which is connected tothe same side of the alternating current source as the anode of theupper diode section. From this it will be apparent that the negativepower supply conductor 62 is common to the separate positive powersupply conductors 6I and I89. A filter condenser II! is connectedbetween positive power supply conductor I69 and negative conductor 62.

Upon th energization of relay I65, a holding circuit is completed fromthe negative power supply conductor 62 over conductor II2, conductor 3I2in Fig. 3, normally closed key BIS, conductor 3M, conductor I I4, frontcontact, lower armature and winding of relay I06, resistor I61 andconductor I08 to the positive power supply conductor I09. The selectordisc contact arm leaves the contact IBI upon receipt of the next signaltransition, thereby interrupting the energizing circuit of relay I06.However, the relay has already established its holding circuit, andremains energized until that circuit is released. The relay I66 alsocompletes a circuit from one terminal of the secondary-winding of abuzzer operating transformer I I6, the primary of which is connectedacross the source of alternating current, over conductor II'I, conductor3I'I, buzzer 3I8, conductor 3I9, conductor II9, front contact and upperarmature of relay I66, conductor I2I, conductor 32I, and conductor I22to the other terminal of the secondary of transformer H6. The operationof buzzer 3I8 indicates to an attendant at the station shown in Fig. 2that intercommunication between the principal station II shown in Fig. 1and the subordinate station 38 shown in Fig. 2 is desired. Accordingly,the attendant momentarily opens key 3I3 to release relay I66, therebystopping the operation of buzzer 3I8, and closes switch 52 to start theoperating motor 51 for the printing telegraph receiver and recorder atstation 38. The attendant at the station 38 in Fig. 2 may thereuponoperate transmitting contacts 48 by mean of keyboard control mechanismshown in the Morton patents hereinbefore identified to transmitpermutation code telegraph signals over line conductors I2 and I3indicative of the fact that the station 38 is in condition to receiveand transmit telegraph signals. Since the selected station call hascaused the buzzer at station 38 in Fig. 2 only to operate, the operatingmotors for the telegraph recorders and transmitters at all otheroutlying stations should be idle and only the principal station II andthe subordinate station 38 will be operative to transmit and recordtelegraph message material.

Since the permutation code telegraph signals involve spacing impulseswhich are much shorter than the spacing impulses of the selectivestation calling codes, the armature of the signal responsive relay 49which follows the permutation code signals will engage its spacingcontact for very much shorter intervals than it did during the receptionof the selective station calling code, and relay 11 will be released forcorrespondingly shorter intervals. The charging current for condenser 32flowing through resistor 83 during these short intervals will berelatively high and will produce a correspondingly high voltage acrosscondenser 84 so that when the lower armature of relay 'I'I engages itsfront contact followin the first short spacing signal impressed upon theline conductorsIZ and I3, the potential of the grid of tube Bl will bemade sufiiciently positive with respect to the cathode to render tube 81conductive. The space discharge path of tube 81 extends from positivepower supply conductor 6I through the winding of a relay I26, conductorsI21 and I28, anode to cathode discharge space of tube 81, conductor I29,resistor 89, conductors 93 and 92 and lower armature and back contact ofrelay ill to negative power supply conductor 62. The relay I26 willbecome energized over this circuit and will remain energized through aholding circuit from positive power supply conductor 6i through thewinding, lower armature and front contact of relay I26 and resistor I3Ito the negative power supply conductor 62. At its upper armature and.front contact the relay I26 prepares an energizing circuit for therelays 68 and ill in series which may be traced from the negative powersupply conductor 62 over conductor I32, winding of relay 9|, conductorI33, winding of relay 68, resistor I34, conductor I36, upper armatureand front contact of relay I26 and conductors I2 and "II to the armatureof signal responsive relay 49. Upon engagement of the armature of relay49 with its marking contact following the spacing signal interval inwhich tube 81 was actuated, the circuit just traced is completed to thepositive power supply terminal 6| and. relays 68 and Ill becomeenergized.

At its upper armature the relay 68 interrupts the circuit from its backcontact through the winding of relay TI to negative power supplyconductor 62 and establishes a circuit through its front contact,resistor I34, winding of relay 68, conductor I33, winding of relay 9|and conductor I32 to negative power supply conductor 62, thusestablishing a holding circuit for the relays 68 and 9|. This holdingcircuit derives its positive power supply connection through thearmature of relay 49 which oscillates in response to the signalsimpressed upon line conductors I2 and I3 but relays 68 and BI haveslow-release characteristics which are sufiiciently slow that they willnot release during the longest spacing interval normally occurring inpermutation code signals but will release in response only to longspacing signals, such as may be impressed upon the line conductors bybreak key I6 at station I I. At its lower armature the relay 68disconnects operating magnet 66 of the step-by-step selector 61 from thenegative power supply conductor 62 so that the magnet will be preventedfrom attempting to operate the selector in response to the permutationcode signals which signal responsive relay 49 follows, thereby estoppingfalse and undesired operation of the step-by-step selector.

With relay 9| energized the positive power supply conductor 6| isconnected over the outer upper armature and front contact to the lowerarmature of relay I26 which is connected to the winding of thatarmature, thus short circuiting the winding and releasing the relay I26.At its lower armature relay 9! interrupts the connection from thenegative power supply conductor 62 to the cathode of discharge tube 8'!thus preventing the further flow of discharge current through that tube.The inner upper armature of relay BI, is connected through resistor MIand glow lamp I42 to the positive power supply will be completed fromnegative power supply conductor 62 through check pawl I02 and theselector disc contact arm, conductors I59 and 459, winding of relay 40!,resistor 408, conductor 409 to positive power supply conductor I09whereby relay 40I will be energized to interrupt the holding circuit forrelays I41 and I06 which will release, thereby interrupting at twopoints the controlling circuit for remotely controllable device 453.

It will be understood that remotely controllable device 453 may havesome other function than controlling motor switch 52 and it may bedesired that such other operation be initiated and terminated beforetelegraphic communication begins, in which case such operation may beterminated under the control of the attendant at station I I, after theoperation has been in process of performance for a suitable interval, bythe transmission of the necessary selective calling code for advancingthe selector disc contact arm to contact I58 before the transmission oftelegraph signals has been started and therefore before selector I58 hasbeen disabled. For example, the operation to be performed might be thecompletion of a buzzer circuit for notifying the attendant at station 38to operate motor switch 52 manually. Instead of having the disablementof the buzzer controlled locally at station 38 as in Fig. 3, the buzzercould be released by the release of relays I41 and I06 under the controlof relay 4IlI after it had been permitted to operate for an intervalwhich the attendant at station II considered adequate.

When a subordinate station is equipped with selector controlledapparatus as shown in Fig. 5, the operation of two remotely controllabledevices may be selectively initiated and terminated. For this purpose, aconductive path extends from selector contact I! over conductors I03,503 and I46 to the winding of relay I41, and when the selector disccontact arm is advanced into engagement with contact IOI theenergizingcircuit for relay I41 will be completed. 'The lower armatureof relay I41 completes a holding circuit over conductors I49,;549, 5I2and H2 to negative power supply conductor 62. I'he upper armature andfront contact of relay I41 complete an operating circuit for a remotelycontrollable device 50I, over conductors I52 and 552 to one terminal ofdevice 56I and over conductors I54 and 554 to the other terminal of thatdevice.

From the contact I56 a conductive path extends over conductors I51, 551and I04 over which the energizing circuit for relay I06 may becompleted. The lower armature of relay I06 completes a holding circuitover conductors I I4, 5I4, 5| 2 and M2 to negative power supplyconductor 62. The upper armature of relay I06 completes an operatingcircuit for a remotely controllable device 502 over conductors H9 and 5|9 to one terminal of device 502 and over conductors I2I and 52I to theother terminal of device 562.

For releasing relay I41 to terminate the operation of remotelycontrollable device 50!, contact I58 of selector 61 is connected overconductors I59, 559 and I6I to the positive terminal of the winding ofrelay I41, and when the selector disc contact arm is advanced byappropriate selective calling signals into engagement with contact I58,a circuit is completed from the negative power supply conductor 62 inshunt relation to the holding circuit for relay I41, whereby the relayis released to terminate the operation of remotely controllable device50I. Similarly a contact I62 of selector 61 is connected throughconductors I63, 563 and I64 to the positive terminal of relay I06, sothat when the selector disc contact arm is advanced into engagement withcontact I52 the holding circuit for relay I06 is shunted by a directconnection to the negative power supply conductor 62, relay I66 isreleased and the operation of selectively controllable device 502 isterminated.

It will be understood that other outlying stations in the system, suchas the stations 3'6 and 31 shown in Fig. 1, are identical with thestation shown in Fig. 2 and will have, in addition to the step-by-stepselectors 58 and 59 at the stations 36 and 31, respectively, electrondischarge tube and relay systems for controlling the conditioning anddisablement of the selectors. It will also be understood that such otherstations may be equipped with selector controlled apparatus according toFig. 3, Fig. 4 or Fig. 5 as desired.

Although particular embodiments of the invention have been shown in thedrawings and described in the foregoing specification, it will beunderstood that the invention is not limited to such specificembodiments but is capable of modification and rearrangement withoutdeparting from the spirit of the invention and within the scope of theappended claims.

What is claimed is:

1. In a selective station calling system, a first station includingmeans for transmitting rapid telegraph signals and means fortransmitting slower station calling signals, a second station includinga relay responsive to both of said types of signals, a selectormechanism controlled by said relay, a slow-release relay energizable todisable said selector mechanism and releasable in response to a longspacing signal to restore said selector mechanism to operativecondition, and means operable in response to rapid telegraph signals foroperating said slow-release relay.

2. In a selective station calling system, a first station includingmeans for transmitting rapid telegraph signals and means fortransmitting slower station calling signals, a second station includinga relay responsive to both of said types of signals, a selectormechanism controlled by said relay, a slow-release relay operable todisable said selector and releasable to restore said selector tooperative condition, a timing relay operable by said signal responsiverelay, and means controlled by said timing relay in response to rapidtelegraph signals for operating said slow-release relay.

3. In a selective station calling system, a first station includingmeans for transmitting rapid telegraph signals and means fortransmitting slower station calling signals, a second station includinga relay responsive to both types of signals, a selector mechanismcontrolled by said relay, a slow-release relay energizable to disablesaid selector and releasable to restore said selector to operativecondition, a timing relay controlled by station including means fortransmitting rapid telegraph signals and means for transmitting slowerstation calling signals, a second station including a relay responsiveto both of said types of signals, a selector controlled by said relay, a

slow-release relay energizable t disable said selector and releasable torestore said selector to operative condition, a timing relay controlledby said signal responsive relay, timing means controlled by said timingrelay, a normally non-conductive discharge tube rendered conductivebysaid timing means, and means controlledby said discharge tube foroperating said slow-release relay.

5. In a selective station call-ing system, a first station includingmeans for transmitting rapid telegraph signals and means fortransmitting slower station calling signals, a second station ineludinga relay responsive to both of said types of signals, a selectorcontrolled by said relay, a slow-release relay energizable to disablesaid selector and releasable to restore the selector to operativecondition, a timing relay controlled by said signal responsive relay,timing means including a i normally non-conductive electron dischargetube controlled by said timing relay in response to rapid telegraphsignals for rendering said tube conductive, and a relay operable by saidtube for energizing said slow-release relay.

6. In a selective station calling system,a first station including meansfor transmitting rapid telegraph signals and means for transmittingslower station calling signals, a second. station including a relayresponsive to both of said types of signals, a selector controlled bysaid relay, a slow-release relay energizable to disable said selectorandreleasable .to restore said selector to operative condition, a timingrelay controlled by said signal responsive relay, timing means includeing a normally non-conductive electron discharge tube controlled by saidtiming relay for rendering said tube conductive inresponse to rapidtelegraph signals, a relay operable by saiddischarge tube for energizingsaid slow-release relay, means controlled by the relay operated by saidtube for establishing its own holding circuit, a relay ener sizableconcurrently with said slow-release relay, and means controlled by saidconcurrently energizable relay for disabling said holding circuit.

7. In a selective station calling system, a first station includingmeans for transmitting rapid telegraph signals and means fortransmitting slower station calling" signals, a second station includinga relay responsive to both of said types of signals, a selectorcontrolled by said relay, a slow-release relay energizable to disablesaid se lector and releasable to restore said selector to operablecondition, a timin relay operable by said signal responsive relay,timing means including a normally non-conductive electron discharge tubecontrolled by said timing relay in. response to rapid telegraph signalsfor rendering said tube conductive, a relay controlled by said tube forenergizing said slow-release relay, and a relay energizable concurrentlywith said slow-release said tube for energizing said slow-release relay,

a relay energizable concurrently with said slow-. release relay,;and anindicating instrumentality controlled by said concurrently operablerelay so as to operate according to one characteristic when'said relayis energized and according to another characteristicwhen said relay isreleased. l i

i 9. In a selective station calling system, a first station includingmeans for transmitting rapid telegraph signals and means fortransmitting slower station calling signals, a second station includinga relay responsive to both of said types of signals, a selectormechanism controlled by said relay, a slow-release relay energizable todisable said selector and releasable to restore said selector tooperative condition, means controlled by said signal responsive relay inresponse torapid telegraph signals for energizing said slow-releaserelay, an indicator lamp, a source of operating current for said lamp,and means associated with said slow-release relay for connecting saidlamp to said source of current steadily when said slow-release relay isreleased and forconnecting said lamp to said source of current throughand under the control of said signal responsive relay when saidslow-release relay is energized whereby the operation ofsaid lampcorresponds to theoperation of said signal responsive relay.

10; In a communication system, a first station including means fortransmitting rapid telegraph signals and means for transmitting slowerstation calling ignals, a second station including a relay responsive toboth of said types of signals, a signal responsive selector mechanismcontrolled by said relay, a slow-release relay energizable to disablesaid selector mechanism and releasable to restore said selectormechanism to operative condition, said slow-release relay having areleasing time longer than spacing intervals normally occurring in saidrapid telegraph signals, means controlled by said signal responsiverelay in response to rapid telegraph signals for completing theenergizing circuit of said slow-release relay, and means associated withsaid slow-release relay for establishing a holding circuit thereforthrough the armature of said signal responsive relay to the markingcontact whereby said slow-release relay is released only upon responseof said signal responsive relay to a continuous spacing signal of aduration at least as long as the release time of said slow-releaserelay.

11. In a selective station calling system, a

' first station including means for transmitting rapid telegraph signalsandmeans for transmitting slower station calling signals, a secondstation including a relay responsive to both of said types of signals,a, selector controlled by said relay, a slow-release relay energizableto disable said selector and releasable to restore said selector tooperable condition, a condenser having a resistor in series therewith,said condenser being chargeable through said resistor and dischargeableindependently of said resistor under the control of said signalresponsive relay,

discharge tube controlled by said timing relay to render said tubeconductive in response to rapid telegraph signals, a relay controlled bya second condenser chargeable in accordance with the current throughsaid resistor, 9, nornals, and a relay operable by said tube for'energizing said slow-release relay.

12. In a selective station calling system, a station having means fortransmitting rapid telegraph signals .and slower station callingsignals, a station having a relay responsive to both types of signals, aslow-release relay having a holding circuit releasably by said signalresponsive relay, a selector mechanism operable by said signalresponsive relay through a back contact of said slow-release relay, andmeans responsive to rapid telegraph signal operation of said signalresponsive relay and unresponsive to slower station calling signaloperation of said signal responsive relay for energizing saidslowrelease raly whereby to disable said selector mechanism.

13. In a selective station calling system, a station having means fortransmitting rapid telegraph signals and slowerstation calling signals,a station having a relay responsive to both types of signals, aslow-release relay having a holding circuit including an armature andfront contact thereof and the armature and marking contact of saidsignal responsive relay, a selector mechanism operable by said signalresponsive relay through an armature and back contact of saidslow-release relay, and means responsive to rapid telegraph signaloperation of said sign-a1 responsive relay and unresponsive to slowerstation calling signal operation of said signal responsive relay forenergizing said slow-release relay whereby to disable said selectormechanism.

14. In a selective station calling system, a station having means fortransmitting rapid telegraph signals and slower station calling signals,a station having a relay responsive to both types of signals, a selectormechanism controllable by said signal responsive relay, a relayenergizable to disable said selector mechanism and releasable to restoresaid selector mechanism to operability, a direct current relay operableby said signal responsive relay, means controlled by said direct currentrelay vfor accumulating electrical potentials in inverse relation to theduration of pulses received by said signal responsive relay, and meanoperable .by an .accumulated potential corresponding to a received pulseof shortlduration for causing said disabling relay to be energized.

15.. In a selective station calling system, a station having means fortransmitting rapid telegraph signals and slower station calling signals,a station having a relay .responsive to both types of signals, aselector mechanism controllable by said signal responsive relay, a relayenergizable to disable said selector mechanism and releasable to restoresaid selector mechanism to operability, a direct current relay operableby said signal responsive relay, a resistance and condenser networkassociated with the contacts of said direct current relay, and meanscontrolled by a condenser ,of said network upon rapid operation of saidrelay in response to rapid telegraph signal operation of said signalrespons sive relay for energizing said disabling relay.

ALLAN WEAVER.

